Cracking hydrocarbon oils



CRACKING HYDROCARBON OILS Filed June 29, 1937 wscas/rraitmvyagrrpcnupza/L 1. 167/ f an: 04 c/ucmva @011.

INVENTOR ROBERTE/PUT/llPl/FF ATTORNEY Patented July 9, 1940 UNITEDSTATES CRAOKIN G HYDBOCABBON OILS Robert F. Ruthnifl', Nutley, N. J.,.asaignor to Standard Oil Company. Chicago, 111., a corporation ofIndiana ap i'icaiionsune 29, 1931. serial No. 150,894

2 Claims.

This invention relates to certain new and useful improvements incombination cracking processes. The invention has in view the provisionof a-combination process in which the constituent elements of the crudepetroleum are treated in a practical way in a complete unitary operationwhich shall be highly eflicient in attainin the ultimate object of amaximum yield of gasoline of maximum anti-knock quality.

In accordance with the invention crude petroleum is subjected tofractionation to separate it into a residue which is subjected toviscositybreaking and into a plurality of condensate or distillatefractions which are subjected to sep arate cracking treatments. Theproducts of the viscosity-breaking operation are fractionated separatelyfrom the products of the other cracking operations so as to thussegregate the rela- .tively low anti-knock viscosity-broken gasoline aswell as other distillates for cracking in the several cracking units ofthe system. The crude residuum is subjected to cracking underviscositybreaking conditions in a single-pass or oncethrough operationand the gas oil constituents produced in the viscosity-breakingoperation are for breaking operations subjected to cracking in anotherrecycling cracking zone, the products from both cracking zones beingfractionated to form a primary reflux condensate which is cycled to theheavygas oil cracking zone and a secondary reflux condensate which iscycled to the light gas oil cracking zone. In this method of operationthe fractions directed into the light gas oil cracking zone may wellinclude gasoline constituents so that the reforming of the gasolineconstituents may be accomplished.

In a modification contemplated by the invention the gasolineconstituents of the crude oil as well as gasoline constituents producedin the viscosity-breaking operation, instead of being included in thecharge to the light gas oil cracking zone, are directed into a separatereforming zone in which the gasoline constituents are subjected toreforming conditions in a single-pass or oncethrough cracking operation.The once-through reforming operation is advantageous in accomplishingthe desired extent of reforming while avoiding deterioration inanti-knock value of reformed constituents. The reformed products may besubjected to fractionation together with the cracked products from thelight gas oil and heavy gas oil cracking zones and thus the distillatepolymer products formed in the reforming operation will be cycled toeither the light gas oil or heavy gas oil cracking zones, where they maybe subjected to further cracking more advantageously-than by cyclingthem to the reforming zone.

15 In order to explain the invention in greater detail, reference willnow be had to the accompanying drawing which is a flow diagramillustrating the invention.

Referring to the flow diagram, heated crude oil which has ben raised toa desired distilling temperature, as by means of heat exchange ofcracked products from the process or by heating in an economizer sectionof the furnaces supplying heat to the cracking coils, is intoducedthrough line It into an evaporator and fractionating tower II. The toweris provided with trap-out trays as l2, II and H for the collection ofthe desired fractions and with a condenser coil l5 and receiving drum itfor the overhead distillate.

Residue from the tower H is withdrawn by a pump I1 and charged to aviscosity-breaking coil l8 positioned in a furnace IS. Theviscositybroken products pass to a separator 20 from which the separatedvapors pass to a series of fractionating towers 2!, 22 and 23, overheadvapors from the last tower passing to a condenser coil 24 discharginginto a distillate receiving drum 2!.

Primary reflux condensate such as gas oil is withdrawn from trap-outtray l2 of tower II by means of line 26 and pump 21 and charged to acracking coil 28 positioned in furnace 29. Primary reflux condensatefrom the viscosity-breaking operation is withdrawn from primary tower 2|by means of line 30 and pump 3| for introduction tothe heating coil 28.The cracked products from the cracking coil 28 pass through transferline 32 to a separator 33.

Secondary reflux condensate such as light gas oil is withdrawn fromtrap-out tray ii of the stripping tower II by means of line 34 and pump35 and charged to cracking coil 36 positioned in furnace 31. Secondaryreflux condensate from u the viscosity-breaking operation is withdrawnfrom tower 22 by means of line 38 and pump 88.

and charged to the heating coil 36. The stocks charged to cracking coil36 should be stocks that are substantially completely vaporizable sothat they will be well adapted for vapor phase cracking under conditionsof high rates of cracking per pass to effect conversion into gasolineconstituents. of high anti-knock value. In the vapor phase crackingoperation it is advantageous to operate with a reaction chamber in whichthe products which have been heated to a high crack- 'ing temperature inthe heating coil may be subjected to further conversion, and accordinglythe transfer line 40 from the vapor phase cracking coil 36 preferablyextends to a reaction chamber 41 from which a transfer line 42 leads tothe separator 33.

A naphtha or gasoline fraction is withdrawn from trap-out tray i4 of thecrude fractionating tower by means of line 43 and pump 44 and charged toa naphtha reforming coil 45 positioned in furnace 46. The line 43 isprovided with a branch line 41 for drawing distillate from receivingdrum [8 for introduction to the reforming coil 45. A naphtha or gasolinefraction is withdrawn from the tertiary fractionating tower 23 of theviscosity-breaking unit by means of a line 48 and pump 48 and charged tothe heating coil 45. A branch line 58 extends to receiving drum 25 forwithdrawing distillate for introduction to the heating coil 45. Atransfer line conducts the products from the naphtha reforming coil 45to the separator 33.

The separated vapors from the evaporator 83 pass to a primaryfractionating tower 52 and a secondary fractionating tower 53, theoverhead vapors from which are condensed in condensing coil 54,discharging into a distillate receiver or gas separator 55. Primaryreflux condensate is withdrawn from tower 52 by means of line 58 andpump 51 and conducted to the recycling cracking coil 28. Secondaryreflux condensate is withdrawn from tower 53 by means of line 58 andpump 59 and conducted to the recycling cracking coil 35.

In one method of practicing the invention the single-pass reforming coil45 is not employed and in this method of operation the charging stockintroduced to the light gas oil cracking or vapor phase cracking coil 35may advantageously contain gasoline constituents which it is desired toreform. For this operation-:ross-ove'r line 80 is provided so thatgasoline fractions from trapout tray l4, as well as distillate fromreceiving drum i6, may be added to the fractions withdrawn from trap-outtray I3 for introduction into the cracking coil 36. If desired, insteadof making the two cuts at trap-out trays l3 and I4, a single cutcomprising light gas oil and gasoline constituents may be withdrawn fromthe tower ii for introduction to the cracking coil 36. For addinggasoline stock to the charge introduced by pump 39 to the cracking coil38, a cross-over line 8i is provided. In this way the relatively lowanti-knock naphtha or gasoline products produced in theviscosity-breaking operation may be combined with the lightviscosity-breaker gas oil. Thus the gasoline or naphtha condensatecollected at the bottom of tower 23, as well as light distillatecollected in receiving drum 25, may be introduced into the cracking coil38. If desired, the tower 28 may be dispensed with and a single cutwithdrawn from tower 22 containing gas oil and gasoline constituentsdirected into the cracking coil 38.

In a modification of the invention the naphtha reforming coil 45 isemployed to subject to reforming the gasoline constituents separatedfrom the crude oil charge, and also, if desired, the gasolineconstituents separated from the viscositybroken products. In this methodof operation the reduced crude is subjected to viscosity-breaking incracking coil l8, primary reflux condensate from trap-out tray I2 oftower Ii and primary reflux condensate from tower 2| is subjected tocracking in heating coil 28, secondary reflux condensate from trap-outtray l3 of tower H and secondary reflux condensate from tower 22 issubjected to cracking in vapor phase cracking coil 35, and gasoline ornaphtha fractions, as withdrawn from trap-out tray ll of tower II, orgasoline or naphtha distillate from receiver i5, is subjected toreforming conditions in cracking coil 45; and gasoline or naphthafractions produced in the viscosity-breaking operation, as withdrawnfrom tower 23 or from receiver 25. may also be subjected to reforming incracking coil 25. The heavy gas oil cracking coil 28 and the light gasoil cracking coil 38 are-operated under recycling conditions. primaryreflux condensate from tower 52 being cycled to cracking coil 28 andsecondary reflux condensate from tower 58 being cycled to cracking coil38. The

viscosity-breaking coil i8 is operated under single-pass conditions, thecondensates formed in tower 2| and- 22 being directed to cracking coil28 and 38 respectively. The naphtha reforming coil 45 is likewiseoperated under single-pass cracking conditions.

In practicing the invention the reduced crude is subjected totemperatures approximating 860 925' F. ,inthe viscosity-breaking coil l8under conditions to effect about 10 percent of cracking per passasmeasured by conversion into 400 F. endpoint gasoline. Under theseconditions there is a relatively large conversion into intermediateconstituents of the nature of gas oil, particularly light gas oilconstituents. The viscosity-breaking operation is advantageously carriedon under pressures of about 100-200 pounds. The cracking of the heavygas oil con stituents in the recycling cracking coil 28 is carried on attemperatures of about 9004000 F. but under a limitation as to the timeof reaction so as to effect about 15 percent cracking per pass. Thepressures employed in the cracking coil 28 are preferably about 300400pounds, although higher pressures even up to as high as 1000 pounds maybe used. Cracking in the cracking coil 38 is carried on at temperaturesof about 9004000 F. with conditions of 20 to percent cracking per passand under pressures preferably of about 200-400 pounds pressure. Whennot using the naphtha reforming coil 45, and when the charge to thecracking coil 38 includes material quantities of gasoline constituents,the cracktration, it should be understood that various modifications andadaptations thereof which will be obvious to one skilled in the art, maybe made within the spirit and scope of the invention gasolineconstituents, subjecting said liquid residue to single-pass cracking ina viscositybreaking zone wherein the liquid residue is sub-.

jected to cracking temperature under viscositybreaking conditions toeffect conversion into a relatively large yield of intermediateconstituents and a smaller yield of gasoline constituents, pass- 1 ingthe resultant viscosity-broken products into a first separating zonewherein vapors separate from residue, fra'ctionating the separatedvapors in a, first fractionating zone to form a heavy reflux condensate,an intermediate reflux condensate and a lighter fraction containinggasoll line constituents, combining said heavy condensate with'saidheavy reflux condensate and subjecting the combined oils to crackingconditions of temperature and pressure in a first recycling crackingzone, combining said intermediate condensate with said intermediaterefiux condensate and subjecting" the combined oils to crackingconditions of temperature and pressure in a second recycling crackingzone, combining said lighter fractions containing gasoline constituentsand subjecting the fractions thus combined to single-pass cracking in aoncethrough reforming zone wherein the gasoline constituents aresubjected to cracking conditions of temperature and pressure adequate toefiect reforming of gasoline constituents into com ponents of increasedanti-knock value, passing the resultant cracked products from both ofsaid recycling cracking zones and from said oncethrough reforming zoneinto a common separating zone, separate from said first separating zone,wherein vapors separate from residue, fractionating the separated vaporsin a second fractionating zone to form a heavier cycle condensate, anintermediate cycle condensate and a final gasoline distillate, directingsaid heavier cycle condensate to said first recycling cracking zone, anddirecting said intermediate cycle condensate to said'second recyclingcracking zone.

-2.' In the cracking of hydrocarbon oils, the process that comprisessubjecting crude petroleum to fractional distillation to form a liquidresidue, a heavy condensate, an intermediate condensate and a lighterfraction containing gasoline constituents, subjecting said liquidresidue to single-pass cracking in a viscosity-breaking zone wherein theliquid residue is subjected to cracking temperatureunderviscosity-breakingconditions to eifect conversion into a relativelylarge yield of intermediate constituents and a smaller yield of gasolineconstituents, passing the resultant viscosity-broken products into aseparating zone wherein vapors separate from residue, fractionating theseparated vapors in a first fractionating zone to form a heavy refluxcondensate and a lighter condensate, combining said heavy condensatewith said heavy reflux condensate and, subjecting the combined oils tocracking conditions of temperature and pressure in a first recyclingcracking zone, combining said intermediate condensate from thefractional distillation of the crude petroleum with said lightercondensate from the viscosity-broken products and subjecting thecombined oils to cracking conditions of temperature and pressure in a\second recycling cracking zone, subjecting said lighter fractioncontaining gasoline constituents to single-pass cracking in aonce-through re-' forming zone wherein the gasoline constituents aresubjected to cracking conditions of temperature and pressure adequate toeffect reforming of gasoline constituents into components of increasedanti-knock value, separating the resultant cracked products from both ofsaid recycling cracking zones and from' said oncethrough reformingzoneinto vapors and residue,

fractionating the separated vapors in a second

